Recently, high packing density of microcircuitry becomes increasingly important as the complexity of electronic equipment advances. In general, monolithic semiconductor integrated circuit chips such as, for example, large scale integration (LSI) chips are housed in solid packages to prevent them from contamination or oxidation resulting from exposure to moisture or harmful gases. The greater the packing density, or the greater the function of microcircuitry, the greater is the number of terminals for external connection of the semiconductor chips. Thus, there is an increasing demand for developments of packages with a number of terminals.
To this end ceramic pin grid array packages with 70 and more terminals have been developed and widely used for packaging of multifunction semiconductor chips and large integration (LSI) chips. However, such ceramic packages make it difficult to take measures to meet the tendency in development of the microcircuitries toward increasing functions and complexity. The ceramic packages must have a relatively large thickness because of their low resistance to mechanical shocks, resulting in increase in size of the packages and semiconductor devices. This also causes increase in weight of the packages since they are generally made of alumina with a relatively large specific gravity.
Since the ceramic pin grid array packages are manufactured by firing ceramic green sheets at a sufficiently high temperature to mature the solid bodies, shrinkage and warping can occur during their firing process. The volume shrinkage varies from about 15 to 20%, thus making it difficult to manufacture packages with high accuracy. The shrinkage of the ceramic body also causes shortcircuiting or breakage of conductor patterns formed thereon, and such troubles increase with the reduction in width of conductor patterns or with the increase in wiring density of the conductor patterns.
Further, the conductor patterns are fired to a sintering temperature of the ceramic body so that they are required to have a high resistance to oxidation and a high melting point. These requirements are fully met only by noble metals such as gold or platinum, thus making it difficult to cut down the manufacturing cost of the packages.
The alumina ceramics for pin grid array packages has a thermal coefficient of linear expansion of 6.8 ppm/.degree.C. which is about 2.5 times as large as a silicon wafer for semiconductor chip production. Such a considerable difference in the thermal expansion coefficient can lead to cracking or damage of the semiconductor chips mounted on the ceramic package since an amount of heat generated in the semiconductor chip increases with the packing density and functions of microcircuitry. Such defect is amplified by low thermal conductivity of the ceramics.
In addition, a manufacturing process of ceramic pin grid array packages is very complicated. For example, the terminal pins must be soldered to proper plated through holes with silver solder at a relatively high temperature of 800 .degree. C. A metal or ceramic lid must be attached to the package by the use of sealing material such as sealing glass or resins to protect the semiconductor chip from contamination or oxidation resulting from exposure to moisture or gases.
To solve these problems, various plastic plug-in type packages have been proposed in a plurality of patent specifications such as, for example, Japanese Patent Laid Open Nos. 60-59756, 60-95943, 60-95944, 60-101998 and 60-111489. Such plastic plug-in type packages are generally manufactured by printed circuit techniques in which conductor patterns are formed in a predetermined design on a surface or surfaces of a common board made of a resin to prepare a single-sided or double-sided printed circuit board.
The use of such a printed circuit board makes it possible to reduce the manufacturing cost and the weight of the packages. However, such plastic plug-in type packages for semiconductor devices have such a problem that the conductor patterns formed on the board are exposed to moisture or gases at the ends of the package, resulting in shortcircuiting or corrosion of the conductor patterns. In addition, it is not possible with the printed circuit board to effectively dissipate the heat generated in the semiconductor chips.